Neuronal cell death can occur through two principal mechanisms: necrosis and apoptosis. Caspase-family proteases are the major effectors of the apoptotic program family. Pathological activation of Caspases has been demonstrated in models of brain injury, including ischemia, neurodegeneration, and neuroinflammation, making these proteases targets for potential drug discovery. Because the human genome contains 11 Caspases, however, a challenge is defining which of these proteases are critical for neuronal cell death in vivo. Caspase-8 is the apical protease in a cell death pathway activated by Tumor Necrosis Factor (TNF) family cytokine receptors. Circumstantial evidence has implicated Caspase-8 in neuronal cell death during ischemia and certain neurodegenerative conditions. Calpains are also intracellular cysteine proteases, which are activated by elevations in intracellular Ca 2+ and which have been implicated in neuronal cell death in models of ischemia and some neurodegenerative diseases. Interestingly, Calpains and Caspases cleave many of the same substrates, implying common or redundant cell death mechanisms. The human genome contains 12 Calpain-family proteases, with Calpains 1 and 2 being most clearly implicated in neuronal cell death. Attempts to directly evaluate the importance of Caspase-8 and Calpains in neuronal cell death in vivo have been hampered by the embryonic lethality that occurs upon knocking-out these genes in mice. We therefore propose to use cre-lox technology for achieving neuron-specific ablation in mice of the genes encoding Caspase-8 and the common subunit shared by Calpains 1 and 2 (capn4). These animals and cells derived from them will then be used for determining the importance of these proteases for neuronal cell death induced by cerebral ischemia and in certain neurodegenerative diseases.